Internal bead forging device for continuous welded tube mill

ABSTRACT

A forging assembly for the continuous flattening of the longitudinal, internal weld bead of small diameter tubing produced by a continuous tube mill. The forging assembly comprises a support roll for the tubing, a mandrel mounted within the tubing, and forging means adapted to impart periodic, overlapping blows so as to flatten the internal bead against the mandrel. The forging means comprises a plurality of planetary forging rolls carried by a roll cage rotatively mounted on a driven race. There is a time delay between each contact of the tube by a forging roll, sufficient to enable the mandrel to engage a new portion of the bead for forging.

nited States aten Follstaedt et al. 51 Jan. 18, 1972 [54] INTERNAL BEADFORGING DEVICE 1,436,062 11/1922 Sussman ..22s/24 FOR CONTINUOUS WELDEDTUBE 1,884,467 10/1932 Windsor ..228/l9 X MILL 2,036,673 4/1936 Anderson..228/24 x [72] Inventors: Donald W. Follstaedt; Robert S. Burns,Primary ExaminerJ0hn F. Campbell both of Middletown, Ohio AssistantExaminer--R. J. Craig [73] Assignee: Armco Steel Corporation,Middletown, Atwmey MelvlneStrasserFostersafioffman 57 ABSTRACT [22]Flled: May 1970 A forging assembly for the continuous flattening of theion- [21] Appl. No.: 35,330 itudinal, internal weld bead of smalldiameter tubin g 8 produced by a continuous tube mill. The forgingassembly comprises a support roll for the tubing, 21 mandrel mountedCCll ..228/24, 22845273i within the tubing, and forging means adapted toimpart 58] Fieid 219/62 periodic, overlapping blows so as to flatten theinternal bead I33 against the mandrel. The forging means comprises aplurality of planetary forging rolls carried by a roll cage rotativelymounted on a driven race. There is a time delay between each [56]References Cited contact of the tube by a forging roll, sufficient toenable the UNITED STATES PATENTS mandrel to engage a new portion of thebead for forging.

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M MugZ M ATTORNEYS INTERNAL READ FORGING DEVICE FOR CONTINUOUS WELDEDTUBE MILL BACKGROUND OF THE INVENTION the flattening of the longitudinalweld bead in the interiorof welded tubing, and more particularly to aforging assembly for use with small diameter welded tubing.

2. Description of the Prior Art In the usual practice wherein flat stripis continuously passed through roll stands which bend the strip intotubular form having a longitudinal seam, the seam is welded by acontinuous welding device, producing both an internal and anexternalbead along the welded seam. The external bead, being.

readilyaccessible, is relatively easily removed or flattenedby a numberof well-known expedients, such as planing, grinding, or passing thetubing through a reducing stand. Under some circumstances, the removalof the external bead (as by flattening or the like) will increase thesize of the internal bead.

When the tube is made of sufficiently soft materialand has asufficiently large internal diameter, the internal bead can also beremoved by rolling or the like. Prior art workers have developed meanscarrying one or morev flattening rolls which may be located within thetubing when the diameter is sufficiently large and which will flattenthe internal-bead in tubing made of hard material such as stainlesssteel or the like. However, considerable difficulty is encountered whentheintemal weld bead is to be removed from tubing of stainless steel orother hard material, having an internal diameter of Ba inches or less.Under such circumstances, the internaldiameter of the tubingis too smallto permit the use of internally locatedflattening rolls.

When the tubing is of hard material and small. internal diameter, priorart workers have turned to the use of an internal anvil within the tubeand means for imparting blows to the exterior of the tube against theanvil so as to flatten theinternal bead. In some instances, hammer.means have been used to impart the blows against an axially movableanvil, as is exemplified in U.S. Pat. No. 2,712,249, in the name of W.Siegerist, and entitled Machine For Flattening Internal Beads In WeldingTube. Hammer-type devices have, however, been characterized by a verycomplex construction.

Prior art workers have also employed work rolls to impart periodic blowsto the external surface of tubing. In general, the work rolls arejournaled in a driven rotatin gfrarne or cage. U.S. Pat. No. 1,436,062,in the name of M. H. Sussman, and entitled Apparatus For WeldingJoints," is exemplary of this construction. Such an assembly, however,requires fullcapacity bearings on each work roll, capable ofwithstandingthe full force on the work rolls during the forgingoperation.

The present invention is directed to a planetary'type forging means fora forging assembly wherein a plurality of planetary forging rolls isrotatively mounted in a roll cage. Therollcage, in turn, is rotativelymounted on a driven race. It has been discovered that such a structuremay bemade more compact while maintaining the ability to deliver blowswith the same force as more bulky prior art structures. The number ofimpacts per given length of tubing may be readily varied, as may be thenumber of rolls in the roll cage. Thereis no need to provide fullcapacity bearings for each of theforging rolls since they are backed bythe race. Finally, the forging means of the present invention displayssmoother running characteristics than prior art forging devices.

SUMMARY OF THE INVENTION The present invention contemplates a forgingassemblyfor flattening an internal, longitudinalweld bead in tubing, andparticularly tubing of small diameter. The forging assembly iscontinuous in action and may constitute a part of a continuous weldedtube mill.

The forging assembly comprises a support roll contacting the exterior ofthe tube opposite the longitudinal weld seam.

The support roll may be an idler roll, or it may be driven so as to'havethe same surface speed as the continuously moving tube. A mandrelis located within the tube. The mandrel has an appropriate worksurfacethereon and, in its normal position, the work surface of themandrel is located above the tangent point between the tube and thesupport roll. The mandrel is normally mounted on a fixed supportalthoughan axiallymovable anvil as shown in U.S. Pat. No. 2,712,249 may be used.

On the opposite side of the tube from the support roll, there is locateda forging means which includes a driven race. The axis of the race shaftis parallel to the axis of the support roll shaft and lies in a planeperpendicular to the tube axis. The race supports a plurality of forgingrolls which are located in a cage. The forging rolls are freelyrotatable on the race and carry the roll cage with them as they roll.

The raceis rotated at such a speed that successive impacts from theindividual planetary forging rolls will produce overlapping deformationsin the tube as it passes through the forging assembly. The planetaryrolls depress the tube surface in an elastic manner so as to flattentheinternal weld bead against the work surface of the mandrel. As aplanetary forging roll contacts the exterior surface of the tube anddepresses it so that the interior weld bead will contact. the mandrel,the mandrel will deform the interior bead to essentially match thecurvature of the tube.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a semidiagrammaticrepresentation of a continuous millfor the production of welded tube,and includes the forging assembly of the present invention.

FIG. 2 is a fragmentary cross-sectional elevation of the forgingassembly of the present invention.

FIG. 3 is a fragmentary view, with parts in cross section, illustratingthe race and the roll cage. 7

FIG. 4 is a fragmentary perspective viewof the roll cage and illustratesthe forging rolls and spacer means.

FIG. 5 is a fragmentary diagrammatic representation of the race, one ofthe planetary forging rolls and the tube, and illustrates the entryangle of the planetary forging roll;

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a semidiagrammaticrepresentation of a tube mill for the continuous production of weldedtube of the type having a continuous longitudinal weld seam. Flatmetallic strip material 1 is caused to pass through a series of rollstands, generally indicated at 2 through 6. The number and nature of theroll stands does not constitute a limitation on the present inventionand are well within the skill of the worker in the art. The roll stands2 through 6 bend the flatstrip 1 into a tubular configuration, generallyindicated at 7. By the time the tubing exits the final forming rollstand 6, it will have a substantially circular configuration with alongitudinally extending seam closed by the rolls of roll stand 6.

Thereafter, the longitudinal tube seam is welded by a continuous weldingmeans 8. Again, the nature of the welding means 8 does not constitute alimitation on the present invention, the welding being accomplished byany suitable process known in the art, such as resistance welding, thegas shielded metal are process, or the like.

As indicated above, the welding process will form both an external andan internal bead along the longitudinal welded seam of the tube. Theexternal bead, beingreadily accessible, may be removed or flattened byany suitable means. For example, when the nature of the tube materialwill permit, the bead may be removed by a planingtool or a grindingmeans. When the tube material is very strong or tough, such as in thecase of stainless steel or the like, the extemalbead may be flattenedbypassing the tube through a reducing or sizing stand. Such a reducing orsizing stand is generally indicated at 9 in FIG. 1.

Next, the tube passes through the forging assembly of the presentinvention for the removal of the internal weld bead. Briefly, theforging assembly comprises a support roll 10, an internal mandrel l1,and a forging means which includes a race 12, a roll cage 13 andplanetary forging rolls 14-17.

The mandrel 11 is supported by elongated means 18, affixed to bracket19. The forging rolls 14-17 are freely rotatable in the cage 13. Thecage, in turn, is freely rotatable on the race 12. The race shaft 12a isconnected to the shaft 20 of a motor means 21 through a conventionaltransmission means, shown in dotted lines at 22. It will be understoodby one skilled in the art that the means and manner by which the race isdriven does not constitute a limitation on the present invention. Forexample, the race shaft may be connected to the shaft of a prime moverby chain means, belt means, or the like. In any event, it is preferableto have means whereby the speed of rotation of the race may be varied.

After the forging operation, the tube 7 will generally be passed througha plurality of sizing stands for the purpose of achieving the desiredfinal tube diameter. The number and nature of the sizing stands does notconstitute a limitation on the invention. For purposes of an exemplaryshowing, three conventional sizing stands are diagrammaticallyrepresented at 23, 24 and 25.

The forging assembly of the present invention is most clearly shown inFIG. 2. Like parts have been given like index numerals. The tube 7 willmove continuously in the direction of arrow A. The tube 7 will besupported by support roll 10, which is preferably concave to match theradius of the tube. The support roll 10 may be an idler roll, or it maybe driven so as to have a surface speed equal to the speed of the tube7. This would prevent slippage between the tube 7 and the support roll.

FIG. 2 also most clearly illustrates the mandrel 11. The mandrel 11 willhave a tapered end 11a and a cylindrical work surface 11b. The other end110 of the mandrel may also by cylindrical and constitute a continuationof the work surface 11b, or it may be tapered in the manner shown withrespect to end 11a so that the mandrel may be reversed end for end forlonger like. The work surface 1 lb will have a diameter smaller than theinternal diameter of the tube 7 by an amount equal to the maximumthickness of the internal weld bead 7a plus clearance, so that themandrel may readily slide within the continuously moving tube.

The mandrel may be made of any suitable hard and wear-resistantmaterial. Excellent results have, for example, been achieved with atungsten carbide mandrel.

In FIG. 2, the mandrel 11 is illustrated in its normal position. In thisposition, the work surface 11b of the mandrel overlies the tangent point10a between the support roll 10 and the tube 7. The mandrel is held inthis position by an elongated means 18. In this instance, the elongatedmeans is illustrated as being a rod. It will be understood by oneskilled in the art that a cable and other elongated means could be used.

The mandrel 11 is afi'rxed to one end of the rod 18 in any suitablemanner (not shown). For example, the end of the rod 18 may be threadedand received in a threaded perforation in the mandrel. Alternatively, areduced diameter portion of the rod may extend through the mandrel witha bolt or other fastening means on the free end .-thereof. The other endof the rod 18 is affixed to bracket means 19. The bracket 19 may befastened to any stationary object (not shown). As will be evident fromFIG. 1, the bracket 19 is located ahead of roll stand 6, the roll standwhich closes the longitudinal seam in the tube 7.

The rod 18 is illustrated as having a reduced portion 180 passingthrough perforation 19a in the bracket 19. The reduced portion 18a isthreaded to receive a nut 26. The shoulder 18b on the rod 18 is heldagainst the bracket 19 by tightening the nut 26. Thus, the mandrel 11 isheld in its proper location except for possible elastic elongation ofthe rod lti during periods ofimpuct.

The race 12 is clearly shown in FIGS. 2 and 3. The race is nonrotativelyaffixed to a race shaft 12a. The axis of the race shaft is parallel tothe axis of the shaft 10b of the support roll 10 and lies in a planeperpendicular to the axis of the tubes (see FIG. 1).

The race 12 supports the roll cage 13. As will be evident from FIGS. 2,3 and 4, the roll cage 13 is made up of two circular elements 13a and13b. The elements 13a and 131; are held in spaced relationship by aplurality of spacer means, four of which are shown at 29-32 in FIG. 2.It will be understood by one skilled in the art that any appropriatetype and any appropriate number of spacer means may be used, so long asthey are uniformly arranged between the circular cage elements 13a and13b. For purposes of an exemplary showing, the spacer means 29 isillustrated in FIG. 4 as comprising a rodlike member. The ends of therodlike member are of reduced diameter and pass through perforations inthe ole ments 13a and 13b. The end portions extending beyond theelements and 13b are adapted to receive fastening means such as the nut33. It is preferable that the spacer means be detachable from at leastone of the circular members 13a and 13b so that the roll cage may bedisassembled for purposes of changing the number of rolls and replacingworn rolls.

FIG. 3 shows forging roll 16 having a shaft 160. The end of the shaftpass through perforations in the circular cage elements 13a 13b. Theroll 16, itself, is backed by the race 12 so that full capacity bearingsneed not be provided for roll shaft 16a.

It will be understood by one skilled in the art that the remainder ofthe forging rolls will be mounted in the same way as shown with respectto roll 16. Additional coaxial holes may be provided in and evenlyspaced about roll cage elements 13a and 13b so that additional forgingrolls may be added to the roll cage as described.

It will be noted that the circular elements 13a and 13b of the roll cageare so sized as to overlap the sides of the race 12. Thus, although theroll cage assembly is freely rotatable about the race 12, it iscaptively held thereon by virtue of the abovementioned overlap.

The operation of the forging assembly of the present invention may bedescribed as follows. The tube 7 will move smoothly and continuouslythrough the forging assembly, the support roll 10 rotating at the samesurface speed as the tube.

As the tube 7 passes through the forging assembly, the race 12 will bedriven by the prime mover 21. The race may be driven in eitherrotational direction. For purposes of an exemplary showing, it may beassumed that the race is driven in a clockwise direction, as viewed inFIG. 2. As a consequence, the roll cage 13 will tend to revolve aboutthe race in a clockwise direction, and the forging rolls 14-17 will tendto revolve in a counterclockwise direction. The race is driven at such aspeed that the successive impacts of the individual planetary rolls onthe tube 7 will produce overlapping deformations in the tube as it movesforwardly. Thus, the rotational speed of the race will depend upon thenumber of planetary forging rolls provided, the diameter of the race andthe size of the work surface 11b on the mandrel, and the speed of thetube.

The diameter of the race 12 and the diameter of the planetary forgingrolls must be selected so that the entry angle of the forging rolls is15 or less. This insures that the planetary forging rolls will enter thespace between the race and the tube 7. Otherwise, the leading one of theforging rolls would simply slide with respect to the race and the tube,remaining stationary at the point where it was tangent with both. Thisis illustrated in FIG. 5 wherein like parts have been given like indexnumerals. The angle of entry B is that angle formed between the surfaceof the tube 7 and the tangent between the forging roll 16 and the race12 when the forging roll first contacts both the race and the tubesurface. Thus, angle B should be 15 or less.

The rotational speed of the race need not be synchronized with theforward speed of the tube 7 since the roll cage and the planetaryforging rolls will assume the proper orbital velocity of their ownaccord. Thus,- the number of impacts imparted to the tubeby the forgingrolls can be varied by changing the rotational speed of the race or thespeed of the tube 7. The cage and the forging rolls will beself-synchronizing. The planetary forging rolls will assume the samesurface speed as the race thereby preventing slippage therebetween.

It is necessary that the planetary forging rolls contact the tubesurface over an area larger than the mandrel work surface 11b, so thatthe plastic deformation occurs on the inside of the tube. The planetaryforging rolls merely depress the tube surface in an elastic manner so asto deform the internal weld head.

The elastic deformation of the tube is such as to cause it to assume anelliptical cross-sectional configuration. The elastic deformation of thetube is not great in amount, and for purposes of clarity has not beenillustrated in FIGS. 1 and 2. Nevertheless, it is preferable that thesurfaces of the support roll and the planetary forging rolls whichcontact the tube will be so shaped as to conform to the ellipticalcross-sectional configuration achieved during maximum impact. Since theamount of elastic deformation is small, the concave surfaces on thesupport roll and the planetary forging rolls can be configured in crosssection as arcs of circles approximating the. elliptical cross-sectionalconfiguration achieved by the tube.

As one of the planetary forging rolls contacts the exterior tube surfaceand depresses it, the top and bottom of the mandrel will be engaged bythe internal weld bead and the interior surface of the tube,respectively. The race, roll cage, and planetary forging rolls must beso sized and arranged that the tube is contacted by only one fofgingroll at a time, with a time delay between contacts. This time delay needonly be sufficient to enable an undeformed portion of the bead to engagethe mandrel. Thus, a forging operation is achieved instead of drawing aswould occur if constant pressure were applied by the forging rolls.

in accordance with the above description, and by virtue of the face thatsuccessive blows to the tube are overlapping, it will be understood thatthe forging assembly of the present inventionwill uniformly flatten theinternal weld bead to confonn to the internal diameter of the tube.While not so limited in its use, the forging assembly of the presentinventionis particularly advantageous for the flattening of internalweld beads in tubes having an internal diameter of 1% inches or less.

Modifications may be made in the invention without departing from thespirit of it. For example, it is within the scope of the presentinvention to provide a work surface on both the top and bottom of theanvil which will approximate the maximum elliptical cross-sectionalconfiguration achieved by the interior surface of the tube duringimpact. 1

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A continuous acting forging assembly for flattening an internal,longitudinal weld head in tubing, which comprises:

a. a support roll contacting the exterior surface of the tube oppositethe longitudinal weld seam; b. a mandrel located within the tube, saidmandrel having a work surface thereon which in its normal positionoverlies the tangent point between said support roll and the tube; andc. forging means including i. a driven race on the opposite side of saidtlibefrom said support roll, the axis of said race being substantiallyparallel to the axis of said support roll and lying in a planeperpendicular to the axis of said tube;

ii. a roll cage supported by said race, said roll cage being tube as itpasses through saidforging assembly;

whereby as said forging rolls contact the exterior surface of said tubeand depresses it in an elastic manner, said mandrel will deform andflatten the internal weld bead of said tube so that it substantiallyconforms to the inside diameterof said tube.

2. The forging assembly according to claim 1, wherein said support rollcomprises an idler roll.

3. The forging assembly according to claim 1, wherein said support rollis rotated at the same surface speed as said tube so asto preventslippage between said tube and said support roll.

4. The forging assembly according to claim 1, wherein said mandrel ismounted on a fixed support.

5. The forging assembly according to claim I, wherein said mandrelcomprise an axially movable anvil.

6. The forging assembly according to claim 1, wherein said mandrel isprovided with a tapered end and said work surface is cylindrical andprovided with a diameter smaller than the internal diameter of said tubeby an amount equal to the maximum thickness of the internal weld beadplus clearance, whereby said tube may readily slide over said mandrel.

7. The forging assembly according to claim 6, wherein said mandrel ismade of tungsten carbide.

8. The forging assembly according to claim 6, wherein the other end ofsaid mandrel is also cylindrical and constitutes a continuation of saidwork surface.

' 9. The forging assembly according to claim 6, wherein the I other endof said mandrel is tapered so that said mandrel may freely rotatableabout said race but captively held thereon;

iii. a plurality of planetary forging rolls located insaid cage, saidforging rolls being freely rotatable on said race and carrying said rollcage therewith; and

iv. means to rotate said race at such a speed that successive impactsfrom said forging rolls will produce overlapping deformation in said bereversed end for end for longer life.

10. The forging assembly according to claim 6, wherein said mandrel ispositioned within said tube by an elongated rod, one end of which isreceived in said mandrel and the other end of which is affixed tobracket means.

11. The forging assembly according to claim 1, wherein said roll cagecomprises two circular elements which are held in spaced relationship bya plurality of spacer means uniformly arranged therebetween, and whereinsaid circular elements overlap the sides of said race, whereby said rollcage is freely rotatable about said race but is captively held thereonby said overlap.

12. The forging assembly according to claim 1, wherein the diameter ofsaid race and the diameter of said forging roll are selected so that theangle formed between the exterior surface of said tube and the tangentbetween one of said forging rolls and said race when said forging rollfirst contacts both said race and the exterior surface of said tube doesnot exceed substantially 15, whereby to insure that said forging rollswill enter the space between said race and said tube.

13. The forging assembly according to claim 12, wherein said forgingrolls contact the exterior surface of said tube over an area larger thanthe work surface of said mandrel so as to ensure that plasticdeformation occurs on the inside surface of said tube.

14. The forging assembly according to claim 13, wherein said race, saidroll cage and said forging rolls are sized and arranged so that saidtube is contacted by only one of said forging rolls at a time, with atime delay between contacts, to enable an undeformed portion of saidinternal bead to engage said mandrel.

15. In a tube mill for the continuous production of welded tubing havingan internal, longitudinal weld bead, of the type having a plurality ofroll stands for bending flat metallic strip material into a tubularconfiguration with a longitudinally extending seam, continuous weldingmeans for welding said longitudinal tube seam, and a forging assemblyfor removing the internal weld bead from said longitudinal tube scam,the improvement in combination therewith, wherein said forging assemblycomprises:

a. a support roll contacting the exterior surface of the tube oppositethe longitudinal weld seam;

b. a mandrel located within the tube, said mandrel having a work surfacethereon which in its normal position overlies the tangent point betweensaid support roll and the tube; and

c. forging means including 7 8 i. a driven race on the opposite side ofsaid tube from said iv. means to rotate said race at such a speed thatsuccessupport roll, the axis of said race being substantially siveimpacts from said forging rolls will produce over- Pamllel to axls ofsaid f p f and lying m a lapping deformation in said tube as it passesthrough plane perpendicular to the axis of said tube; Said f i assembly;

ii. a roll cage supported by said race, said roll cage being freelyrotatable about said race but captively held thereon;

iii. a plurality of planetary forging rolls located in said cage, saidforging rolls being freely rotatable on said race and carrying said rollcage therewith; and 10 5 whereby as said forging rolls contact theexterior surface of said tube and depress it in an elastic manner, saidmandrel will deform and flatten the internal weld bead of said tube sothat it substantially conforms to the inside diameter of said tube.

1. A continuous acting forging assembly for flattening an internal,longitudinal weld bead in tubing, which comprises: a. a support rollcontacting the exterior surface of the tube opposite the longitudinalweld seam; b. a mandrel located within the tube, said mandrel having awork surface thereon which in its normal position overlies the tangentpoint between said support roll and the tube; and c. forging meansincluding i. a driven race on the opposite side of said tube from saidsupport roll, the axis of said race being substantially parallel to theaxis of said support roll and lying in a plane perpendicular to the axisof said tube; ii. a roll cage supported by said race, said roll cagebeing freely rotatable about said race but captively held thereon; iii.a plurality of planetary forging rolls located in said cage, saidforging rolls being freely rotatable on said race and carrying said rollcage therewith; and iv. means to rotate said race at such a speed thatsuccessive impacts from said forging rolls will produce overlappingdeformation in said tube as it passes through said forging assembly;whereby as said forging rolls contact the exterior surface of said tubeand depresses it in an elastic manner, said mandrel will deform andflatten the internal weld bead of said tube so that it substantiallyconforms to the inside diameter of said tube.
 2. The forging assemblyaccording to claim 1, wherein said support roll comprises an idler roll.3. The forging assembly according to claim 1, wherein said support rollis rotated at the same surface speed as said tube so as to preventslippage between said tube and said support roll.
 4. The forgingassembly according to claim 1, wherein said mandrel is mounted on afixed support.
 5. The forging assembly according to claim 1, whereinsaid mandrel comprise an axially movable anvil.
 6. The forging assemblyaccording to claim 1, wherein said mandrel is provided with a taperedend and said work surface is cylindrical and provided with a diametersmaller than the internal diameter of said tube by an amount equal tothe maximum thickness of the internal weld bead plus clearance, wherebysaid tube may readily slide over said mandrel.
 7. The forging assemblyaccording to claim 6, wherein said mandrel is made of tungsten carbide.8. The forging assembly according to claim 6, wherein the other end ofsaid mandrel is also cylindrical and constitutes a continuation of saidwork surface.
 9. The forging assembly according to claim 6, wherein theother end of said mandrel is tapered so that said mandrel may bereversed end for end for longer life.
 10. The forging assembly accordingto claim 6, wherein said mandrel is positioned within said tube by anelongated rod, one end of which is received in said mandrel and theother end of which is affixed to bracket means.
 11. The forging assemblyaccording to claim 1, wherein said rolL cage comprises two circularelements which are held in spaced relationship by a plurality of spacermeans uniformly arranged therebetween, and wherein said circularelements overlap the sides of said race, whereby said roll cage isfreely rotatable about said race but is captively held thereon by saidoverlap.
 12. The forging assembly according to claim 1, wherein thediameter of said race and the diameter of said forging roll are selectedso that the angle formed between the exterior surface of said tube andthe tangent between one of said forging rolls and said race when saidforging roll first contacts both said race and the exterior surface ofsaid tube does not exceed substantially 15*, whereby to insure that saidforging rolls will enter the space between said race and said tube. 13.The forging assembly according to claim 12, wherein said forging rollscontact the exterior surface of said tube over an area larger than thework surface of said mandrel so as to ensure that plastic deformationoccurs on the inside surface of said tube.
 14. The forging assemblyaccording to claim 13, wherein said race, said roll cage and saidforging rolls are sized and arranged so that said tube is contacted byonly one of said forging rolls at a time, with a time delay betweencontacts, to enable an undeformed portion of said internal bead toengage said mandrel.
 15. In a tube mill for the continuous production ofwelded tubing having an internal, longitudinal weld bead, of the typehaving a plurality of roll stands for bending flat metallic stripmaterial into a tubular configuration with a longitudinally extendingseam, continuous welding means for welding said longitudinal tube seam,and a forging assembly for removing the internal weld bead from saidlongitudinal tube seam, the improvement in combination therewith,wherein said forging assembly comprises: a. a support roll contactingthe exterior surface of the tube opposite the longitudinal weld seam; b.a mandrel located within the tube, said mandrel having a work surfacethereon which in its normal position overlies the tangent point betweensaid support roll and the tube; and c. forging means including i. adriven race on the opposite side of said tube from said support roll,the axis of said race being substantially parallel to the axis of saidsupport roll and lying in a plane perpendicular to the axis of saidtube; ii. a roll cage supported by said race, said roll cage beingfreely rotatable about said race but captively held thereon; iii. aplurality of planetary forging rolls located in said cage, said forgingrolls being freely rotatable on said race and carrying said roll cagetherewith; and iv. means to rotate said race at such a speed thatsuccessive impacts from said forging rolls will produce overlappingdeformation in said tube as it passes through said forging assembly;whereby as said forging rolls contact the exterior surface of said tubeand depress it in an elastic manner, said mandrel will deform andflatten the internal weld bead of said tube so that it substantiallyconforms to the inside diameter of said tube.